LOC semiconductor assembled with room temperature adhesive

ABSTRACT

A semiconductor device assembly has a lead frame and a semiconductor device configured to be attached to each other. An adhesive is applied at room temperature through a stencil to the lead frame. The semiconductor device is urged against the adhesive to effect the attachment between the semiconductor device and the lead frame. The adhesive preferably is from about 75 percent to about 95 percent isobutyl acetal diphenol copolymer and from about 25 percent to about 5 percent, respectively, of titanium oxide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of application Ser. No.09/795,889, filed Feb. 28, 2001, pending, which is a continuation ofapplication Ser. No. 09/176,967, filed Oct. 22, 1998, now U.S. Pat. No.6,248,611, issued Jun. 19, 2001, which is a continuation of applicationSer. No. 08/916,977, filed Aug. 14, 1997, now U.S. Pat. No. 5,840,598,issued Nov. 24, 1998.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention: This invention relates to the manufactureof semiconductor device assemblies and, more particularly, to methods ofassembly of semiconductor devices using room temperature adhesives andto the assembled semiconductor device and lead frame using roomtemperature adhesives.

[0003] State of the Art: To manufacture a semiconductor device assembly,a semiconductor device, typically called a die or chip, is typicallyattached to a lead frame. A lead frame is a structure having a pluralityof leads, bus bars, or other connecting structure to be electricallyconnected with the semiconductor device. In a conventional lead frame,the lead frame includes a die paddle to which the semiconductor deviceis attached and a plurality of leads extending inwardly to surround theperiphery of a semiconductor device mounted on the die paddle.Subsequently, a plurality of wire bonds are made to connect the bondpads on the active surface of the semiconductor device to the ends ofthe leads extending around the periphery of the semiconductor device. Ina leads-over-chip type lead frame (LOC lead frame), the lead frame isformed having no die paddle and having a plurality of leads whichextends over the active surface of the semiconductor device beingsecured thereto to support the semiconductor device, with a plurality ofwire bonds being formed between the bond pads on the active surface ofthe semiconductor device and the ends of the leads of the lead frame.

[0004] A conventional lead frame or LOC frame may serve other functions.That is, it may assist in heat dissipation during manufacture, increasethe structural strength of the assembled semiconductor device as well asprovide convenient locations to make electrical connections.

[0005] In order to attach the semiconductor device to the lead frame,different adhesives and adhesively coated tapes have been suggested. Forexample, U.S. Pat. No. 5,304,582 (Ogawa) shows use of adhesive tape withdifferent adhesives on opposite sides for attaching a die to a leadframe. U.S. Pat. No. 5,548,160 (Corbett et al.) discloses use ofadhesives including adhesives that have a core.

[0006] Typically, in attaching a LOC lead frame to a semiconductordevice, a double-coated adhesive tape is applied between the activesurface of the semiconductor device and the lead frame. The adhesivetape is typically an insulating carrier with a polymer adhesive on bothsides to mechanically interconnect the lead frame and the semiconductordevice. The tape composition and the amount of polymer adhesive used onthe tape varies with the size of the semiconductor device. It is desiredto use the least amount of adhesively coated tape to attach asemiconductor device to a lead frame to attempt to minimize problems.Too much polymer adhesive added to the tape can cause a coefficient ofthermal expansion mismatch between the lead frame, the polymer adhesiveand the semiconductor device which can contribute to the failure of thepackaged device. Reducing the size of the tape to enhance performancemay involve reprocessing the tape at some increased cost and at somedifficulty for the smaller sizes. U.S. Pat. No. 5,548,160 (Corbett etal.)

[0007] If an adhesive, as opposed to an adhesively coated tape, is usedto attach the semiconductor device to the lead frame, the quantity ofadhesive must be carefully controlled in the dispensing process. Thebond time for the adhesive is recognized to be difficult to control andcan vary greatly with variations in adhesive viscosity, adhesiveapplication temperature and amount of adhesive used. Further, adhesivecan bleed from under the lead finger and interfere with the attachmentof other lead fingers of the lead frame. Also, use of an adhesive (atelevated temperatures) may also lead to a nonuniform bond line betweenthe semiconductor device and the lead frame. That is, the semiconductordevice is not generally in alignment with the lead frame, causingdifferent spacings to be present between the lead fingers and the bondpads on the active surface of the semiconductor device, therebyaffecting wire bonding operations. Additionally, uneven application ofadhesive or non-uniform adhesive viscosity can lead to tilting of thesemiconductor device relative to the lead frame. An uneven or tiltedrelationship has been determined to be a factor that reducessemiconductor device assembly quality and leads to failures.

[0008] Therefore, an adhesive with better qualities suitable for directbonding of the semiconductor device to the lead fingers of a lead frameis desirable.

BRIEF SUMMARY OF THE INVENTION

[0009] A semiconductor device assembly is formed by joining a lead frameand a semiconductor device. The lead frame includes a plurality of leadfingers, each lead finger having a lower attaching surface for adhesiveattachment to portions of the active surface of a semiconductor device.

[0010] A non-conductive polymer adhesive is selected from the group ofadhesives that is tacky and compliant at room temperature, easilyapplied to a substrate, such as through the use of a stencil, and easilycured to a predetermined degree. The non-conductive polymer is applied,at room temperature, either to the lower surface of the lead fingers ofthe lead frame or to portions of the active surface of the semiconductordevice for compression therebetween. The lead fingers are connected bywire bonds to the bond pads on the active surface of the semiconductordevice.

[0011] The adhesive preferably has a first copolymer material selectedfrom the group of copolymers that includes isobutyl compounds and asecond material that is from a group of metal oxides that includestitanium dioxide. Preferably, the first material is isobutyl acetaldiphenol copolymer. More preferably, the second material is titaniumdioxide.

[0012] In a preferred composition, the adhesive has about 75 percent toabout 95 percent of isobutyl acetal diphenol copolymer and,respectively, from about 25 percent to about 5 percent of titaniumdioxide.

[0013] Methods of assembling the semiconductor device assembly includeproviding a lead frame and a semiconductor device. A non-conductivepolymer adhesive is selected from the group that is tacky and compliantat room temperature and is applicable to a substrate through a stencil.The adhesive is applied to one of the semiconductor device and a surfaceof the lead frame at room temperature. The lead frame and thesemiconductor device are urged together at room temperature to attachthe semiconductor device to the lead frame and with electricalconnections between the lead fingers of the lead frame and the bond padson the active surface of the semiconductor device made by wire bondsextending therebetween.

[0014] In the preferred methods of assembly, the adhesive may be fromthe groups of adhesives as described hereinbefore.

[0015] In an alternate configuration, a stencil is provided with theadhesive, at room temperature, applied to either a surface of each leadfinger of the lead fingers or portions of the active surface of thesemiconductor device. The lead frame and the semiconductor device arethereafter positioned relative to each other and urged together toeffect attachment and electrical connection, if desired.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] In the drawings which illustrate what are regarded as the bestmodes and preferred embodiments for carrying out the invention:

[0017]FIG. 1 is a perspective simplified illustration of a semiconductordevice assembly of the invention;

[0018]FIG. 2 is a perspective simplified illustration of a semiconductordevice assembly of the invention with a stencil for applying adhesive;

[0019]FIG. 3 is a cross sectional depiction of portions of asemiconductor device of the invention; and

[0020]FIG. 4 is a cross sectional depiction of portions of asemiconductor device assembly of the invention with the semiconductordevice and the lead frame in contact.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to drawing FIG. 1, a semiconductor device assembly 10includes a lead frame 12 having a plurality of lead fingers 14 thereon.The lead frame 12 is one of a plurality that is connected in end-to-endfashion, thereby forming a strip or roll of lead frames. That is, leadframe 12 is positioned between a preceding frame 16 and a followingframe 18. The lead frame 12 as well as the preceding frame 16 andfollowing frame 18 are driven or moved through a manufacturingenvironment by an appropriate drive or indexing system that engages theapertures 20 formed in the opposite edges, or rails, 22 and 24. At aconvenient time, the lead frames 12, 16 and 18 are separated one fromthe other and the opposite edges, or rails, 22 and 24 are removed sothat each frame with a semiconductor device attached thereto becomes aseparate and useable semiconductor device assembly.

[0022] Each lead frame 12 is formed having a plurality of lead fingers14, each lead finger 14 having a lower surface, i.e., an undersurface orattaching surface 26. In some instances, the bond pads 36 of thesemiconductor device 34 may include bumps thereon to mate with each ofthe lead fingers 14 of the lead frame 12.

[0023] As illustrated in drawing FIG. 1, the semiconductor device 34 isany suitable semiconductor device configured for attachment to the leadframe 12. The semiconductor device 34 has portions, bond pads 36, on theactive surface thereof configured for electrical connection to the leadfingers 14 of a lead frame 12. As illustrated, the semiconductor device34 has a plurality of bond pads 36 thereon, all suitably positioned sothat, upon proper positioning of the semiconductor device 34 withrespect to the leads of a lead frame, the bond pads 36 are available forfurther connection. The semiconductor device 34 may also have additionalbond pads thereon.

[0024] Adhesive 40 is used to attach the lead frame 12 and thesemiconductor device 34 together. As shown in FIG. 1, the adhesive 40may be applied in a line or in a plurality of beads positioned foreffecting attachment of the semiconductor device 34 to the attachingsurface 26 of the lead fingers 14 of the lead frame 12.

[0025] In operation, the adhesive 40 is preferably applied to anattaching surface 26 of the lead fingers 14 of the lead frame 12. Thatis, the adhesive 40 is positioned on the attaching surface by anyappropriate nozzle, roller, glue gun tip or the like. Upon urging thesemiconductor device 34 and the lead frame 12 together, the adhesive 40is compressed and spread horizontally to effect an attachment. Since theadhesive is preferably at room temperature, viscosity and flow istypically constant throughout the adhesive. In turn, the risk of anuneven relationship between the semiconductor device and the lead frameis reduced as the semiconductor device and lead frame are assembled.Further, application at room temperature of the adhesive reduces heatinduced failures in the semiconductor device and lead frame assemblyarising during the assembly operations.

[0026] As illustrated in drawing FIG. 2, the lead frame 60 is the sameas lead frame 12. The lead frame 60 is positioned to pass relative to astencil 62. That is, a drive or indexing means (not shown) urges thelead frame 60 as well as the preceding frame 64 and the following frame66 to move past the stencil 62. A source 67 of adhesive 68 isillustrated separate from the stencil 62 for clarity. In normal use, thestencil 62 is positioned so that adhesive 68 from the source 67 is urgedthrough the apertures 70 of the stencil 62 (by, for example, a piston)and onto the underside or attachment surface 72 of the lead frame 60.The stencil 62 may be configured with any desired pattern of aperturesfor deposition of adhesive 68 on an attaching surface 72 of the leadframe 60. Of course, the adhesive may also be deposited on the activesurface 73 of the semiconductor device 76.

[0027] The source 67 with stencil 62 and adhesive 68 may move up anddown relative to the attaching surface 72 to apply the adhesive 68thereto. An anvil block 74 may be positioned opposite the stencil 62 sothat the lead frames 60, 64 and 66 are all properly supported uponmovement of the stencil 62 in close proximity and upon operation of thesource 67 to urge the adhesive 68 outwardly to and in contact with theattaching surface 72. A similar anvil block may be positioned so thatthe lead frame 60 is supported upon movement of the semiconductor device76 into contact with the adhesive on the attaching surface 72 of thelead frame 60 and further upon compression of the adhesive 68 as theactive surface 73 of the semiconductor device 76 is urged toward theattaching surface 72 of the lead frame 60. As the active surface 73 ofthe semiconductor device 76 comes into contact with the attachingsurface 72, bond pads 78, 80 and 82 located on the active surface 73 ofthe semiconductor device 76 are positioned to effect electricalconnection with corresponding lead fingers 60′ of the lead frame 60 asdesired using wire bonds.

[0028] Referring to drawing FIG. 3, a semiconductor device 34 isillustrated in relation to the lead fingers 14 of a lead frame 12 havingadhesive 40 applied to the attaching surfaces 26 thereof.

[0029] Referring to drawing FIG. 4, a semiconductor device 34 isillustrated having the active surface 35 thereof secured to theattaching surfaces 26 of the lead fingers 14 of a lead frame 12 (notshown) by the adhesive 40 located therebetween. As previously stated,the adhesive 40 may be applied to either the active surface 35 of thesemiconductor device 34 or the attaching surfaces 26 of the lead fingers14 of a lead frame 12. The lead fingers 14 and the semiconductor device34 are pressed into contact with the adhesive 40, which is subsequentlycured. Also illustrated, wire bonds 100 extend between and electricallyconnect the lead fingers 14 with the bond pads 36 on the active surface35 of the semiconductor device 34.

[0030] The adhesives 40 and 68 are non-conductive polymers selected fromthat group or class of adhesives that is tacky and compliant at roomtemperature and is at the same time applicable at room temperature to asubstrate through a stencil such as stencil 62. The adhesives 40 and 68preferably have a first copolymer that is from the group of copolymersthat includes isobutyl compounds and is specifically isobutyl acetaldiphenol copolymer. The adhesive also contains a second material whichis from a group of metal oxides that includes titanium dioxide. Thepreferred adhesive has from about 75 percent by weight or volume toabout 95 percent by weight or volume of isobutyl acetal diphenolcopolymer and respectively from about 25 percent to about 5 percent byweight or volume of titanium dioxide. The amounts of the twoconstituents may vary somewhat from those stated so long as theresulting composition has the requisite tackiness and compliancy to besuitable to secure a semiconductor device and a lead frame at roomtemperature.

[0031] A suitable adhesive is available from InternationalMicroelectronics Research Corporation of Nampa, Idaho under the productdesignation EXP/NCBP-4143-33 and is also known as NON-CONDUCTIVE BUMPPOLYMER 4243-33 (hereinafter referred to as the BUMP POLYMER). The BUMPPOLYMER is particularly suitable because it may be applied at or nearroom temperature so that assembly can be effected at room temperature.Room temperature is generally deemed to be between 60° Fahrenheit (F.)and 85° F. and may range from as low as 50° F. to as high as 95° F.

[0032] To manufacture the desired semiconductor devices, the userprovides the necessary lead frames in frame by frame sequence. Each leadframe has an attaching surface and connectors associated therewith.Semiconductor devices are also provided in a piece by piece sequence,each to be attached to an appropriate lead frame. Each semiconductordevice has bond pads thereon configured for electrical connection to thelead fingers of its respective lead frame.

[0033] A non-conductive polymer adhesive from the group that is tackyand compliant at room temperature and is applicable through a stencil isselected and applied at room temperature to one of the semiconductordevice and the attaching surface of the lead frame and preferably theattaching surface. The semiconductor device and the attaching surfaceare urged together to effect a desired connection between the activesurface of the semiconductor device and the lead frame. Desirably, theadhesive selected is the isobutyl acetal diphenol copolymer withtitanium dioxide as hereinbefore described. In a preferred method, theadhesive is urged through the stencil as it is applied to the attachingsurface of the lead frame or the active surface of the semiconductordevice.

[0034] As previously stated, wire bonds are used to form the electricalconnections between the ends of the lead fingers of the lead frame andthe bond pads on the active surface of the semiconductor device.

[0035] Those skilled in the art will appreciate that modifications maybe made to the illustrated embodiment and the disclosed methods withoutdeparting from the spirit or principles of the invention and are notintended to limit the scope of the following claims.

What is claimed is:
 1. A method for attaching a semiconductor die havingan active surface to a portion of a lead frame having a plurality oflead fingers thereon, at least one lead finger having an attachingsurface, said method comprising: selecting an adhesive from a group ofadhesives comprising tacky and compliant polymer adhesives at roomtemperature, said polymer adhesive including a first material from agroup that includes isobutyl acetal diphenol copolymer and a secondmaterial that is from a group including metal oxides; applying saidpolymer adhesive in one of at least one line of polymer adhesive and aplurality of beads of polymer adhesive on one of at least a portion ofsaid active surface of said semiconductor die and the attaching surfaceof at least one lead finger, said polymer adhesive at room temperature;and urging said active surface of said semiconductor die with saidattaching surface of said at least one lead finger of said plurality oflead fingers of said lead frame while at room temperature for attachingthe attaching surface of said at least one lead finger of said pluralityof lead fingers of said lead frame and said active surface of saidsemiconductor device.
 2. The method of claim 1, wherein a portion ofsaid polymer adhesive has a first copolymer material from a group ofcopolymers that includes isobutyl compounds.
 3. The method of claim 1,wherein a first portion of said polymer adhesive is isobutyl acetaldiphenol copolymer.
 4. The method of claim 1, wherein said polymeradhesive includes a group of metal oxides that includes titaniumdioxide.
 5. The method of claim 4, wherein said polymer adhesive hasfrom about 75 percent to about 95 percent by weight of isobutyl acetaldiphenol copolymer and from about 25 percent to about 5 percent byweight, respectively, of titanium dioxide.
 6. A method of attaching asemiconductor die to at least a portion of a lead frame, said methodcomprising: providing a lead frame having at least one lead having atleast one attaching surface thereon; providing a semiconductor diehaving an active surface and having at least one bond pad thereon;selecting an adhesive which includes a first material from a group thatincludes an isobutyl acetal diphenol copolymer and a second materialthat is from a group including titanium dioxide; applying said polymeradhesive in one of at least one line of adhesive and a plurality ofbeads of adhesive on at least a portion of said active surface of saidsemiconductor die, said adhesive at room temperature; and urging saidactive surface of said semiconductor die and said attaching surface ofsaid lead frame together to attach said semiconductor die and said leadframe together connecting said attaching surface of said lead frame andsaid active surface of said semiconductor die having a portion of saidat least one lead located adjacent said at least one bond pad on saidactive surface of said semiconductor die.
 7. A method of attaching aportion of a semiconductor die to a portion of a lead frame for use in asemiconductor device assembly, said method comprising: providing a leadframe having a plurality of lead fingers, each lead finger of saidplurality of lead fingers having an attaching surface and an endportion; providing a semiconductor die having an active surface andhaving a plurality of bond pads thereon; selecting an adhesive thatincludes from about 75 percent to about 95 percent of isobutyl acetaldiphenol copolymer and from about 25 percent to about 5 percent,respectively, of titanium dioxide; applying said adhesive in one of aline of adhesive and a plurality of beads of adhesive to at least aportion of said active surface of said semiconductor die, said adhesiveat room temperature; and urging said active surface of saidsemiconductor die and said attaching surfaces of said plurality of leadfingers of said lead frame together at room temperature to attach atleast a portion of said semiconductor die and said lead frame togetherconnecting said attaching surfaces of said lead fingers of saidplurality of lead fingers of said lead frame and said portions of activesurface of said semiconductor die at least some lead fingers of saidplurality of lead fingers having the end portion thereof locatedadjacent a bond pad of said plurality of bond pads of said semiconductordie.
 8. A method of attaching at least a portion of a semiconductor dieto a portion of a lead frame for use in a semiconductor device assembly,said method comprising: providing a lead frame having at least one leadhaving at least one attaching surface; providing a semiconductor devicehaving an attaching surface and having at least one bond pad; providinga stencil having a pattern therein; selecting a polymer adhesive from agroup that is tacky and compliant at room temperature for application toa substrate using a stencil; applying said polymer adhesive in one of atleast one line of adhesive and a plurality of beads of adhesive to aportion of said attaching surface of said semiconductor device throughsaid stencil, said adhesive at room temperature; positioning said atleast one attaching surface of said lead frame and said attachingsurface of said semiconductor device relative to each other; and urgingsaid attaching surface of said semiconductor device and said at leastone attaching surface of said lead frame together to attach saidsemiconductor device and said lead frame together having a portion ofsaid at least one lead of said lead frame located adjacent said at leastone bond pad of said semiconductor die.
 9. A method of attaching atleast a portion of a semiconductor die to a portion of a lead frame foruse in a semiconductor device assembly, said method comprising:providing a lead frame having at least one lead having at least oneattaching surface; providing a semiconductor device having an attachingsurface and having at least one bond pad; providing a stencil having apattern therein; selecting an adhesive including a first material from agroup that includes isobutyl acetal diphenol copolymer and a secondmaterial that is from a group that includes titanium dioxide; applyingsaid polymer adhesive in one of at least one line of adhesive and aplurality of beads of adhesive through said stencil to at least aportion of said attaching surface of said semiconductor device, saidadhesive at room temperature; positioning said at least one attachingsurface of said lead frame and said attaching surface of saidsemiconductor device relative to each other; and urging said attachingsurface of said semiconductor device and said at least one attachingsurface of said lead frame together at room temperature to attach saidsemiconductor device and said lead frame together having a portion ofsaid at least one lead of said lead frame located adjacent said at leastone bond pad of said semiconductor die.
 10. A method of attaching atleast a portion of a semiconductor die to a portion of a lead frame foruse in a semiconductor device assembly, said method comprising:providing a lead frame having at least one lead having at least oneattaching surface; providing a semiconductor device having an attachingsurface and having at least one bond pad; providing a stencil having apattern therein; selecting an adhesive including from about 75 percentto about 95 percent of isobutyl acetal diphenol copolymer and from about25 percent to about 5 percent, respectively, of titanium dioxide;applying said adhesive through said stencil in one of at least one lineadhesive and a plurality of beads of adhesive to said attaching surfaceof said semiconductor device, said adhesive at room temperature;positioning said lead frame and said semiconductor device relative toeach other; and urging said semiconductor device and said lead frametogether to attach said semiconductor device and said lead frame usingsaid adhesive having a portion of said at least one lead locatedadjacent said at least one bond pad of said semiconductor die.